Papers

Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study
Louise Arseneault, Mary Cannon, Richie Poulton, Robin Murray, Avshalom Caspi, Terrie E Moffitt

Editorial by Rey and
Tennant
Papers pp 1195,
1199

SGDP Research
Centre, King’s
College, London
SE5 8AF
Louise Arseneault lecturer Avshalom Caspi professor Terrie E Moffitt professor Division of
Psychological
Medicine, King’s
College
Mary Cannon
Wellcome Trust advanced fellow
Robin Murray professor Dunedin
Multidisciplinary
Health and
Development
Research Unit,
University of Otago,
Dunedin,
New Zealand
Richie Poulton director, Dunedin multidisciplinary health and development study

The strongest evidence that cannabis use may be a risk factor for later psychosis comes from a Swedish cohort study which found that heavy cannabis use at age 18 increased the risk of later schizophrenia sixfold.1 2 This study could not establish whether adolescent cannabis use was a consequence of pre-existing psychotic symptoms rather than a cause. We present the first prospective longitudinal study of adolescent cannabis use as a risk factor for adult schizophreniform disorder, taking into account childhood psychotic symptoms3 antedating cannabis use.

Methods and results
The Dunedin multidisciplinary health and development study (a study of a general population birth cohort of 1037 individuals born in Dunedin, New Zealand, in 1972-3)4 has a 96% follow up rate at age 26. It obtained information on psychotic symptoms at age
11 and drug use at ages 15 and 18 from self reports and assessed psychiatric symptoms at age 26 with a standardised interview schedule to obtain DSM-IV
(diagnostic and statistical manual of mental disorders,
4th edition) diagnoses. We analysed data from a representative group of 759 (74%) living study members who had